Microlens alignment procedures in cmos image sensor design

ABSTRACT

A method for aligning a microlens array in a sensor die to resolve non-symmetric brightness distribution and color balance of the image captured by the sensor die. The method includes performing a pre-simulation to simulate a microlens array alignment in a silicon die and to determine a shrink-factor and de-centering values, calculating the error in a real product&#39;s alignment in process and image offset, performing a post simulation based on offset calculation on the real product and re-design of the microlens alignment, and repeating the steps of calculating the error and performing the post-simulation until a satisfactory brightness distribution is obtained. The sensor die has sensor pixels, each pixel comprising a photodiode and a microlens for directing incoming light rays to the photodiode, wherein optical axis of the microlens is shifted with respect to optical axis of the photodiode by a preset amount determined by at least one iteration of alignment process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/004,465filed on Dec. 12, 2004.

BACKGROUND

1. Field of the Invention

The present invention relates to CMOS image sensor design and moreparticularly to microlens alignment procedures of CMOS image sensors.

2. Background of the Related Art

There has been an increase of digital image devices using CMOS imagesensors. A conventional CMOS image sensor requires a matching imaginglens to have certain ray angle incident on its sensor surface togenerate acceptable image data output. In an effort to mitigate the rayangle requirement, the CMOS sensor may be customized to accept incidentrays at large angles, especially for the pixels at corners and edgesthereof.

One common practice of CMOS sensor customization is shifting a microlensarray of the sensor to match the incident rays at large angles. However,in the application of the shifting technique, the non-symmetric natureof the CMOS sensor pixel layout may create non-symmetric brightnessdistribution over the image output, where the non-symmetric nature maybe more pronounced at the corners and edges of the image output. Inaddition, such non-symmetric brightness may be accompanied by impropercolor balance, i.e., the color of the image of a white light source isnot white over the entire image output.

To resolve the appearance of non-symmetric brightness distribution overthe image output, the existing approaches have attempted severalsymmetric layouts for each pixel of the CMOS sensor. Such approaches mayimpose many limitations and restrictions to a layout designer and sometradeoff may be necessary to accommodate the symmetric layout withadditional silicon real estate. In addition, the entire CMOS pixellayout may be modified upon unsatisfactory image output, which requireslengthy and expensive turn-around processes. Furthermore, the existingapproaches cannot correct the non-symmetric nature that may be rooted inother sources, such as chemical contamination occurred during the CMOSprocess for producing a silicon die, electrical field generated by metallayers of the CMOS sensor, imperfect masks used in the CMOS process andother unknown sources. Thus, there is a need for an improved method forresolving non-symmetric brightness distribution.

SUMMARY

The present invention provides a method for aligning a microlens arrayin a sensor die to resolve non-symmetric brightness distribution andimproper color balance of images captured by the sensor die.

In one aspect of the present invention, a method for aligning amicrolens array in a sensor die includes the steps of (a) performing apre-simulation to simulate a microlens array alignment in a silicon dieand to determine a shrink-factor; (b) designing a new photo-mask for themicrolens array based on the shrink-factor; (c) producing a samplesilicon die using the new photo-mask; (d) capturing an image of acollimated white light source using the sample silicon die; (e)evaluating uniformity of brightness distribution of the image; and incase of unsatisfactory brightness distribution; (f) calculating error inalignment of the sample silicon die and a de-centering value; (g)performing a post-simulation based on the error to tune theshrink-factor and the de-centering value; (h) designing a new photo-maskfor the microlens array based on the shrink-factor and the de-centeringvalue; and (i) repeating the steps (c)-(h) until a satisfactorybrightness distribution is obtained.

In another aspect of the present invention, a sensor die for digitalimaging includes: a processing area; and a sensing area, comprising: aplurality of sensor pixels, comprising: a silicon substrate having aphotodiode and a plurality of passive components; a first insultinglayer on top of the silicon substrate; a plurality of metal layers ontop of the first insulating layer, the photodiode and the plurality ofpassive components connected to at least one of the plurality of metallayers; a plurality of middle insulating layers, each of the pluralityof middle insulating layers sandwiched between two neighboring ones ofthe plurality of metal layers; a first insulating planar layer on top ofthe plurality of metal layers; a color filter; a second insulatingplanar layer on top of the color filter; and a microlens to directincoming light to the photodiode through the color filter; wherein anoptical axis of the microlens is shifted with respect to an optical axisof the photodiode by a preset amount determined by at least oneiteration of alignment process, each of the at least one iterationincluding a pre-simulation to determine a shrink-factor and apost-simulation to tune the shrink-factor.

In yet another aspect of the present invention, an imaging deviceincludes: a sensor die for digital imaging, comprising: a processingarea; and a sensing area, comprising: a plurality of sensor pixels, eachof the plurality of sensor pixels comprising: a silicon substrate havinga photodiode and a plurality of passive components; a first insultinglayer on top of the silicon substrate; a plurality of metal layers ontop of the first insulating layer, the photodiode and the plurality ofpassive components connected to at least one of the plurality of metallayers; a plurality of middle insulating layers, each of the pluralityof middle insulating layers sandwiched between two neighboring ones ofthe plurality of insulating layers; a first insulating planar layer ontop of the plurality of metal layers; a color filter; a secondinsulating planar layer on top of the color filter; and a microlens todirect incoming light to the photodiode through the color filter;wherein an optical axis of the microlens is shifted with respect to anoptical axis of the photodiode by a preset amount determined by at leastone iterative alignment process, each of the at least one iterativealignment process including a pre-simulation to determine ashrink-factor and a post-simulation to tune the shrink-factor.

In still another aspect of the present invention, a computer readablemedium carries one or more sequences of instructions for aligning amicrolens array in a sensor die, wherein execution of the one or moresequences of instructions by one or more processors causes the one ormore processors to perform the steps of: (a) performing a pre-simulationto simulate a microlens array alignment in a silicon die and todetermine a shrink-factor; (b) designing a new photo-mask for themicrolens array based on the shrink-factor; (c) producing a samplesilicon die using the new photo-mask; (d) capturing an image of acollimated white light source using the sample silicon die; (e)evaluating uniformity of brightness distribution of the image; and incase of unsatisfactory brightness distribution; (f) calculating error inalignment of the sample silicon die and an image de-centering value; (g)performing a post-simulation based on the error to tune theshrink-factor; (h) designing a new photo-mask for the microlens arraybased on the shrink-factor and the de-centering value; and (i) repeatingthe steps (c)-(h) until a satisfactory brightness distribution isobtained.

In another aspect of the present invention, a system for aligning amicrolens array in a sensor die includes: means for performing apre-simulation to simulate a microlens array alignment in a silicon dieand to determine a shrink-factor; means for designing a new photo-maskfor the microlens array based on the shrink-factor; means for producinga sample silicon die using the new photo-mask; means for capturing animage of a collimated white light source using the sample silicon die;means for evaluating uniformity of brightness distribution of the image;and in case of unsatisfactory brightness distribution; means forcalculating error in alignment of the sample silicon die and an imagebrightness center offset; means for performing a post-simulation basedon the error to tune the shrink-factor; means for designing a newphoto-mask for the microlens array based on the shrink-factor and theimage brightness center offset; and means for repeating the steps ofproducing a sample silicon die to the step of designing a new photo-maskuntil a satisfactory brightness distribution is obtained.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an image module assembly in accordancewith one embodiment of the present teachings.

FIG. 2 a is a top view of a portion of a silicon die in accordance withone embodiment of the present teachings.

FIGS. 2 b, 2 c and 2 d are a front, perspective and side view of theportion in FIG.

2 a, respectively

FIG. 3 is a detailed layout of two metal layers and photodiodes inaccordance with one embodiment of the present teachings.

FIGS. 4 a and 4 b illustrate ray acceptance angles for a sensor with anon-shifted microlens array.

FIG. 5 is an image of a white light source captured by an image sensorhaving a sensor die, where the brightness of the image is non-uniformacross the sensor die.

FIGS. 6 a and 6 b illustrate ray acceptance angles for a sensor with ashifted microlens array in accordance with one embodiment of the presentteachings.

FIG. 7 is a top view of a sensor die with a microlens array, elements ofwhich are shifted to achieve ray angle match over the entire sensor diein accordance with one embodiment of the present teachings.

FIG. 8 is a flow chart of an iterative process for aligning a microlensarray in a sensor die in accordance with one embodiment of the presentteachings.

FIG. 9 shows an image captured by a sensor die having a microlens arrayaligned with de-centering offset following the steps in FIG. 8.

DETAILED DESCRIPTION

Foregoing described embodiments of the invention are provided asillustrations and descriptions. They are not intended to limit theinvention to precise form described. In particular, it is contemplatedthat functional implementation of invention described herein may beimplemented equivalently in hardware, software, firmware, and/or otheravailable functional components or building blocks. Other variations andembodiments are possible in light of above teachings, and it is thusintended that the scope of invention not be limited by this DetailedDescription, but rather by Claims following.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described.

It must be noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “amicrolens” includes a plurality of such microlens, i.e., microlensarray, and equivalents thereof known to those skilled in the art, and soforth.

One common practice of CMOS sensor customization is shifting a microlensarray of the sensor to match incident rays at large angles. However, inthe application of the shifting technique, the non-symmetric nature ofthe CMOS sensor layout may create non-symmetric brightness distributionover the image output, where the non-symmetric nature may be morepronounced at the corners and edges of the image output. In addition,such non-symmetric brightness may be accompanied by improper colorbalance, i.e., the color of the image of a white light source is notwhite over the entire image output. The present inventor provides asimple, yet effective way to resolve the appearance of non-symmetricbrightness in the image by introducing off-center alignment (alignedwith de-centering values) between a microlens array and a sensor pixelarray of the CMOS sensor.

FIG. 1 is a schematic diagram of an image module assembly 100 (or,equivalently a lens/sensor assembly) in accordance with one embodimentof the present teachings. The lens/sensor assembly 100 may be includedin digital image devices, such as digital image camera and cellularphone with imaging capabilities. As illustrated, the lens/sensorassembly 100 includes: a sensor die 108 as an image sensor; and a lensassembly 102 having several pieces of lenses and iris (no shown in FIG.1 for simplicity) assembled in a lens barrel, the lens assembly formingan image on the surface of the sensor die 108. In one embodiment, thewidth and length of the sensor die 108 is about, but not limited to, 5mm.

Optical rays 104 a-c, exemplary optical rays from the lens assembly 102,are directed to sensor pixels (the sensor pixels will be explainedlater) at the center, near the left edge and near the right edge of thesensor die 108, respectively, and angled with respect to the surfacenormal of the sensor die 108 by chief ray angles 106 a-c, respectively.The chief ray angles 106 b and 106 c may be as large as 30 degrees,while the chief ray angle 106 a is about zero degree.

The sensor die 108, a type of CMOS image sensor, is a piece of siliconthat includes an integrated circuit (IC) to function as an image sensor.The IC comprises a processing area and a sensing area that may have fromseveral hundred thousands to millions of identical sensor pixels.Hereinafter, for simplicity, the sensor die 108 refers to its sensingarea only. FIG. 2 a is a top view of a portion 109 of the silicon die108 in accordance with one embodiment of the present teachings, whereonly 9 sensor pixels 110 are shown for simplicity. FIGS. 2 b and 2 d arethe front and side views of the portion 109 in FIG. 2 a, respectively,showing multiple layers 112-138 of the silicon die 108. FIG. 2 c is aperspective view of the portion 109 in FIG. 2 a, focusing on several keyfeatures of the layers.

As shown in FIGS. 2 b-2 d, each pixel 110 includes: a silicon substratelayer 112; a photodiode 114 forming a portion of and being underneaththe surface of the silicon substrate layer 112; a plurality of passivecomponents 115 (such as transistors, resistors and capacitors)underneath the surface of the silicon substrate layer 112; fourtransparent insulating layers 116, 120, 124 and 128; four metal layers118, 122, 126 and 130, the four metal layers being insulated by the fourtransparent insulating layers 116, 120, 124 and 128, and connected tothe photodiode 114 and/or the plurality of passive elements 115; a firstplanar layer 132, the first planar layer being a transparent insulatinglayer and having a flat top surface; a color filter 134 for passing aspecific wavelength or wavelength band of light to the photodiode 114;and a microlens 138 for focusing light rays to the photodiode 114. Amicrolens array 139 in FIG. 2 c comprises the identical microlens 138.

In one embodiment of the present teachings, the photodiode 114 and theplurality of passive elements 115 may be formed by a semiconductoretching process, i.e., etching the surface of the silicon substratelayer 112 and chemically depositing intended types of material on theetched area to form the photodiode 114 and the plurality of passiveelements 115.

As mentioned, the color filter 134 filters light rays (such as 104 inFIG. 1) directed to its corresponding photodiode 114 and transmits lightrays of only one wavelength or wavelength band. In one embodiment of thepresent teachings, a RGB color system may be used, and consequently, acolor filter array (CFA) 135 (shown in FIG. 2C) comprises three types offilters 134. In the RGB system, signals from three pixels are needed toform one complete color. However, it is noted that the number of typesof filters in the CFA 135 can vary depending on the color system appliedto the silicon die 108.

The metal layers 118, 122, 126 and 130 function as connecting means forthe photodiodes 114 and passive components 115 to the processing area ofthe silicon die 108, where the signals from the photodiodes and passivecomponents are transmitted using a column transfer method. In FIGS. 2 cand 2 d, for the purpose of illustration, exemplary connections 119 and121 are shown, where the connections 119 and 121 link the metal layer118 to the photodiode 114 and one of the passive components 115,respectively. However, it should be apparent to the one of ordinaryskill that connections between the four metal layers (118, 122, 126 and130) and the photodiode 114 and the passive components 115 can varydepending on the overall layout of the silicon die 108. Also, the numberof metal layers depends on the complexity of the layout of metal layersand, as a consequence, a different layout of the silicon die may havedifferent number of metal layers.

FIG. 3 is a detailed layout 300 of the metal layers and photodiodes ofthe silicon die 108 in accordance with one embodiment of the presentteachings, where a top view of only two metal layers 118, 122 andphotodiodes 114 are shown for simplicity. The metal layers 118 and 122may be formed of an opaque material, such as aluminum, and define theshape of openings 302 through which the light rays directed to eachphotodiode 114 are collected. As shown in FIG. 3, the shape of theopening 302 may not have any axis of symmetry. Tn addition, the layoutof two other metal layers 126 and 130, when superimposed on top of thelayout 300, would make the opening 302 be further non-symmetric. Theeffective light collecting area of the non-symmetric opening 302 variesas the angle of light rays with respect to the surface normal of theopening 302 changes. Consequently, the intensity of electric signal fromthe photodiode 114 may be a function of the chief ray angle 106 (shownin FIG. 1).

As illustrated in FIG. 1, each of the optical rays 104 a-c is angledwith respect to the surface normal of the sensor die 108. FIGS. 4 a and4 b illustrate ray acceptance angles 406 for a sensor die 408 with anon-shifted microlens array 404, where the optical axis of a microlensin each pixel 410 coincides with the optical axis of a photodiode 402 inthe pixel. (Hereinafter, the optical axis of a photodiode refers to anaxis normal to the surface of the photodiode and passes through thegeometric center of the photodiode.) In FIGS. 4 a-b, for simplicity,only photodiodes 402 and a microlens array 404 are shown. As illustratedin FIG. 4 a, most of the light rays 104 a are collected by a photodiode402 a that is located at the center of the sensor die 408. Thus, thelight ray acceptance angle 406 a is same as that of incoming light rays104 a. In contrast, as shown in FIG. 4 b, some portion of the opticalrays 104 b are not collected by a photodiode 402 b that is located nearthe right edge of the silicon die 408, i.e., the photodiode 402 b has alimited ray acceptance angle 406 b. Such limited ray acceptance angle,when combined with the non-symmetric nature of the opening 302, mayresult non-uniform brightness distribution of an image on the sensor die408, as shown in FIG. 5. FIG. 5 shows an image 500 of a white lightsource captured by an image sensor having the sensor die 408, where thebrightness of image 500 is non-uniform across the sensor die 408. Inaddition, the image 500 may not be a color balanced, i.e., the color ofthe image is not white over the entire sensor die.

FIGS. 6 a and 6 b illustrate ray acceptance angles 606 for a sensor die608, where the optical axis of a microlens 604 in each pixel 610 hasbeen shifted with respect to the optical axis of a photodiode 602 of thepixel in accordance with one embodiment of the present teachings. InFIG. 6 a, the optical axis of a microlens 604 a in a pixel coincideswith the optical axis of a photodiode 602 a of the same pixel, where thepixel is located at the center of the sensor die 608. However, as shownin FIG. 6 b, the optical axis of a microlens 604 b in a pixel locatednear the right edge of the sensor die 608 has been shifted by a distance612 with respect to the optical axis of a photodiode 602 b in an effortto improve the ray acceptance angle 606 b. The light ray acceptanceangles 606 a and 606 b are equal to those of the incoming light rays 104a and 104 b, respectively.

In this embodiment, a pre-simulation has been performed to calculate thedistance 612 for each pixel 610 and simulate the ray acceptance angles606 by a basic optical method, such as a conventional optical ray tracetechnique. Based on the calculated distance 612, a “shrink-factor” iscalculated, where the shrink-factor is the ratio of the dimension of themicrolens array 604 to that of the silicon die 608. Hereinafter, theterm “shrinking” means reducing the size of microlens array 604 based onthe calculated shrink-factor. Actual shrinking is realized by reducingthe area of each microlens and gaps between neighboring microlenses,while the thickness of the microlens may be kept unchanged. As themicrolens array 604 is formed using a photo-mask in a photo-processingof the silicon die 608, shrinking is implemented by scaling thephoto-mask.

FIG. 7 is a top view of a sensor die 700 with a microlens array 702, theelements of which are shifted to achieve ray angle match over the entiresensor die 700 in accordance with one embodiment of the presentteachings. (In FIG. 7, for simplicity, only the array of microlens 702and photodiodes 704 are shown.) As shown in FIG. 7, each microlens 702has been shifted toward the center 712 of the sensor die 700 so thateach of light spots 706 is located within the corresponding photodiode704, which improves the ray acceptance angle, and subsequently, thebrightness distribution of image on the silicon die 700. The shifting ofeach microlens is more pronounced near sensor edges 710 and corners 708than the center 712. As mentioned above, the shifting of each microlensis implemented by scaling a photo mask of the microlens array 702.

The pre-simulation based on the optical ray trace technique may notprovide a perfect prediction of the optical characteristics of thepixels due to the complexity of the layout of the silicon die. Also, theaccuracy of the pre-simulation is limited as the pixel size keepsshrinking. Furthermore, it is quite difficult, if not possible, tosimulate the effects of additional factors that may contribute tosimulation error. The factors include; chemical contamination occurredduring the CMOS process for producing a silicon die; electrical fieldgenerated by metal layers; and imperfect masks used in the CMOS processas well as other unknown sources. Thus, upon completion of shrinkingbased on the pre-simulation and production of a sample product of thesilicon die, an image of a collimated white light source captured by thesample product should be analyzed to access any error in the samplesilicon die's alignment and image center offset (or, equivalently,de-centering value). If the brightness distribution of the capturedimage of the collimated white light source is not satisfactory, furtheradjustment via an iteration process may be performed.

FIG. 8 is a flow chart 800 of an iterative process for aligning amicrolens array in a sensor die in accordance with one embodiment of thepresent teachings. At step 802, a pre-simulation is performed tosimulate a microlens array alignment and to determine a shrink-factor asdescribed above. Based on the shrink-factor, a new photo-mask for themicrolens array is designed at step 804. Next, a sample silicon die isproduced using the new photo-mask at step 806. Subsequently, an image ofa collimated white light source is captured by the produced samplesilicon die at step 808. At step 810, the uniformity of brightnessdistribution on the captured image is evaluated. In this step, thedistribution of both intensity and color balance of the image areevaluated. In case of unsatisfactory distribution, the error inalignment of the sample silicon die and image center offset can becalculated at step 814. Next, at step 816, based on the calculatederror, post-simulation may be performed in the same manner as thepre-simulation of step 802 to tune the shrink-factor and de-centeringvalues. Subsequently, a new photo-mask for the microlens array isdesigned based on the tuned shrink-factor at step 818 and the steps806-818 are repeated until a satisfactory image is obtained to end theiterative process at step 812.

FIG. 9 shows an image 900 captured by a sensor die having a microlensarray aligned with de-centering following the steps in FIG. 8. As can benoticed, the image 900 shows enhanced uniformity of brightness andsymmetric color balance over the entire sensor die compared to the image500 in FIG. 5. Thus, the iteration process, the steps 806-818 of FIG. 8,allows a sensor designer to tune the shrink-factor in a high precisionand effectively improve the image quality.

Those skilled in the art will appreciate that the methods and designsdescribed above have additional applications and that the relevantapplications are not limited to those specifically recited above. Itshould be understood that the foregoing relates to exemplary embodimentsof the invention and that modifications may be made without departingfrom the spirit and scope of the invention as set forth in the followingclaims

1-8. (canceled)
 9. A method, comprising: capturing an image using afirst image sensor having a first microlens array formed using a firstphoto-mask; generating one or more correction parameters by evaluatingthe captured image; creating a second photo-mask based on the firstphoto-mask and the one or more correction parameters; and using thesecond photo-mask to form a second microlens array of a second imagesensor.
 10. The method of claim 9, further comprising: using acollimated white light source to produce the image captured by the firstimage sensor.
 11. The method of claim 10, wherein said evaluating thecaptured image comprises evaluating a uniformity of brightnessdistribution of the captured image.
 12. The method of claim 9, wherein:said generating one or more correction parameters comprises determininga shrink-factor from the captured image; and said creating a secondphoto-mask comprises shrinking the first photo-mask based on theshrink-factor.
 13. The method of claim 9, wherein: said generating oneor more correction parameters comprises determining a de-centering valuefrom the captured image; and said creating a second photo-mask comprisesde-centering the first photo-mask based on the de-centering value. 14.The method of claim 9, wherein: said generating one or more correctionparameters comprises determining a shrink-factor and a de-centeringvalue from the captured image; and said creating a second photo-maskcomprises: shrinking the first photo-mask based on the shrink-factor;and de-centering the first photo-mask based on the de-centering value.15. The method of claim 10, wherein: said generating one or morecorrection parameters comprises determining a shrink-factor and ade-centering value based on a uniformity of brightness distribution ofthe captured image; and said creating a second photo-mask comprises:shrinking the first photo-mask based on the shrink-factor; andde-centering the first photo-mask based on the de-centering value. 16.An article of manufacture including a computer-readable medium havinginstructions stored thereon that, in response to execution by acomputing device, cause the computing device to perform operationscomprising: receiving image data captured by a first image sensor havinga first microlens array formed using a first photo-mask design;calculating an error in alignment between the first image sensor and thefirst microlens array based on the image data; determining ashrink-factor based on the calculated error in alignment; and generatinga second photo-mask design that corresponds to the first photo-maskdesign shrunken by the shrink-factor.
 17. The article of manufacture ofclaim 16, wherein said calculating an error in alignment comprisesevaluating a uniformity of brightness distribution of the image data.18. The article of manufacture of claim 16, wherein said generating asecond photo-mask design comprises shrinking the first photo-mask designbased on the shrink-factor.
 19. The article of manufacture of claim 16,wherein: said calculating an error in alignment comprises determining ade-centering value from the image data; and said generating a secondphoto-mask design comprises de-centering the first photo-mask designbased on the de-centering value.
 20. The article of manufacture of claim16, wherein: said calculating an error in alignment comprisesdetermining a de-centering value from the image data; and saidgenerating a second photo-mask design comprises: shrinking the firstphoto-mask design based on the shrink-factor; and de-centering the firstphoto-mask design based on the de-centering value.
 21. A method,comprising: using a first photo-mask design to form a first microlensarray on a first sensor die; determining a de-centering value based onimage data from the first image sensor; de-centering the firstphoto-mask design based on the de-centering value to obtain a secondphoto-mask design; and using the second photo-mask design to form asecond microlens array on a second sensor die.
 22. The method of claim21, further comprising: using a collimated white light source to producean image; capturing the image with the first image sensor; andgenerating the image data based on the captured image.
 23. The method ofclaim 22, wherein said determining a de-centering value comprisesevaluating a uniformity of brightness distribution of the capturedimage.
 24. The method of claim 21, further comprising: determining ashrink-factor based on the image data; and shrinking the firstphoto-mask design based on the shrink-factor to obtain the secondphoto-mask design.
 25. A system, comprising: an image source configuredto produce an image; and a computing device configured to: receive imagedata generated by a first image sensor in response to capturing theimage; determine, based on the image data, one or more correctionparameters for a first photo-mask design used to form a first microlensarray on the first image sensor; and create a second photo-mask designfor a second microlens array on a second image sensor based on the firstphoto-mask design and the determined one or more correction parameters.26. The system of claim 25, wherein the image source comprises acollimated white light source.
 27. The system of claim 26, wherein thecomputing device is further configured to determine the one or morecorrection parameters based on a uniformity of brightness distributionof the captured image.
 28. The system of claim 25, wherein the computingdevice is further configured to: determine a shrink-factor of the one ormore correction parameters from the captured image; and shrink the firstphoto-mask design based on the shrink-factor.
 29. The system of claim25, wherein the computing device is further configured to: determine ade-centering value of the one or more correction parameters from thecaptured image; and de-center the first photo-mask design based on thede-centering value.
 30. The system of claim 25, wherein the computingdevice is further configured to: determine a shrink-factor and ade-centering value of the one of more correction parameters from thecaptured image; shrink the first photo-mask based on the shrink factor;and de-center the first photo-mask based on the de-centering value. 31.The system of claim 26, wherein the computing device is furtherconfigured to: determine a shrink-factor and a de-centering value of theone or more correction parameters based on a uniformity of brightnessdistribution of the captured image; shrink the first photo-mask based onthe shrink-factor; and de-center the first photo-mask based on thede-centering value.